From LQWiki

Question: Do you want the background tabs half-covered along the top bar? Because right now they are (at least in Firefox).

Well, they are supposed to be in the "background". The current tab you are in is in a different color and as you mouse over background tabs they come to the foreground. I wasn't a huge fan of that at first, but I have to say it has really grown on me. Jeremy 11:50, March 1, 2007 (EST)